Then it struck my mind, if currently there are plugins that modify text while editing in Sublime Text, it's 'in theory' possible to create a plugin that finds Arabic letters, reverse those words and replace each letter with the correct shape.

However, I'm afraid that doing this may have a side effect on the saved files, since the Arabic-shaping should be used for displaying only and not directly editing the file text. Hence, I have to either reverse the edits before saving a file, or create the plugin in a way that it only changes what you see, not what you type [I'm not sure if I explained this in the right words].